Thermostat metals

ABSTRACT

THERMOSTAT METALS WHICH HAVE HIGH FLEXIVITES ON THE ORDER OF AT LEAST ABOUT 13X10**-7 FOR DISPLAYING SUBSTANTIAL FLEXING MOVEMENT IN RESPONSE TO TEMPERATURE VARIATIONS WITHIN A SELECTED RANGE BUT WHICH ARE ADAPTED TO BE RESTRAINED AGAINST ADDITIONAL FLEXING MOVEMENT WHILE BEING SUBJECTED TO MUCH HIGHER TEMPERATURES WITHOUT TENDING TO BECOME PERMANENTLY DEFORMED ARE SHOWN TO COMPRISE THREE LAYERS OF METAL BONDED TOGETHER, TWO OF THESE METAL LAYERS HAVING RELATIVE THERMAL EXPANSION PROPERTIES, MODULI OF ELASTICITY AND THICKNESSES PROVIDING THE THERMOSTAT METALS WITH THE DESIRED HIGH FLEXIVITES AND THE THIRD LAYER, PREFERABLY OF HIGH STRENGTH STEEL DISPOSED BETWEEN THE TWO OTHER LAYETS, HAVING THERMAL EXPANSION PROPERTIES INTERMEDIATE THE THERMAL EXPANSION PROPERTIES OF THE TWO OTHER LAYERS, AND HAVING MUCH GREATER STRENGTH THAN THE MATERIALS OF EITHER OF TWO TWO OTHER LAYERS. THERMOSTAT METALS CONVENTIONALLY EMBODY METAL LAYERS OF SELECTED ALLOYS WHICH HAVE BEEN ESPECIALLY DEVELOPED TO DISPLAYED VERY HIGH AND VERY LOW COEFFICIENTS OF THERMAL EXPANSION. WHEN THESE METAL LAYERS ARE BONDED TOGETHER IN WORK-HARDENED CONDITION, THE RESULTING THERMOSTAT METALS HAVING HIGH FLEXIVITES AND DISPLAY A SUBSTANTIAL OF SELECTED ALLOYS WHICH HAVE BEEN ESPECIALLY DEVELOPED CHARGES. WHILE SUCH CONVENTIONAL THERMOSTAT METALS ARE WIDELY USEFUL, IT IS FOUND THAT IN SOME APPLICATIONS, WHERE THE THERMOSTAT METALS ARE ARRANGED TO DISPLAY SUBSTANTIAL FLEXING MOVEMENT IN RESPONSE TO TEMPERATURE VARIATIONS WITHIN A SELECTED TEMPERATURE RANGE BUT ARE RESTRAINED AGAINST ADDITIONAL FLEXING MOVEMENT WHILE BEING SUBJECTED TO RELATIVELY HIGHER TEMPERATURES, THE THERMOSTAT METALS TEND TO UNDERGO A CHANGE IN THERMAL RESPONSE CHARACTERISTICS DURING USE, THAT IS, IT IS FOUND THAT STRESSES DEVELOPED IN THE THERMOSTAT METALS WHEN THEY ARE HEATED TO HIGH TEMPERATURE WHILE RESTRAINED AGAINST FLEXING MOVEMENT TEND TO CAUSE A DEGREE OF PERMANENT DEFORMATION IN THE THERMOSTAT METALS.

Aug. 13, 1974 K, CHAREST ETAL 3,829,296

THERMOSTAT uETALs Filed June 26, 1972 United States Patent Othce 3,829,296 Patented Aug. 13, 1974 3,829,296 THERMOSTAT METALS Kenneth Charest, Attleboro, Mass., Robert F. Hanley, Pawtucket, RJ., and Jacob L. Ornstein, Norton, Mass., assignors to Texas Instruments Incorporated, Dallas,

Tex

Filed June 26, 1972, Ser. No. 266,027 Int. Cl. B32b 15/00 U.S. Cl. 29-19S.5 3 Claims ABSTRACT F THE DISCLOSURE Thermostat metals which have high ilexivities on the order of at least about l30 l0*7 for displaying substantial exing movement in response to temperature variations within a selected range but which are adapted to be restrained against additional iiexing movement while being subjected to much higher temperatures without tending to Ibecome permanently deformed are shown to comprise three layers of metal bonded together, two of these metal layers having relative thermal expansion properties, moduli of elasticity and thicknesses providing the thermostat metals with the desired high tlexivities and the third layer, preferably of high strength steel disposed between the two other layers, having thermal expansion properties intermediate the thermal expansion properties of the two other layers, and having much greater strength than the materials of either of the two other layers.

Thermostat metals conventionally embody metal layers of selected alloys which have been especially developed to display very high and very low coeicients of thermal expansion. When these metal layers are bonded together in work-hardened condition, the resulting thermostat metals have high flexivities and display a substantial degree of flexing movement in response to temperature changes. While such conventional thermostat metals are widely useful, it is found that in some applications, where the thermostat metals are arranged to display substantial flexing movement in response to temperature variations within a selected temperature range but are restrained against additional flexing movement while being subjected to relatively higher temperatures, the thermostat metals tend to undergo a change in thermal response characteristics during use. That is, it is found that stresses developed in the thermostat metals when they are heated to high temperature while restrained against flexing movement tend to cause a degree of permanent deformation in the thermostat metals.

It is an object of this invention to provide novel and improved thermostat metals; to provide such improved thermostat metals which display substantial flexing movement in response to temperature variations within a selected temperature range but which are adapted to be restrained against additional exing movement while being subjected to much higher temperatures without tending to become permanently deformed; and to provide such improved thermostat metals at low cost.

Other objects, advantages and details of the thermostat metals of this invention appear in the following detailed description of preferred embodiments of the invention, the detailed description referring to the drawings in which:

FIG. l is a perspective view of a length of thermostat metal provided by this invention.

Referring to the drawings, in FIG. 1 indicates the novel and improved composite thermostat metal provided by this invention which is shown to include a rst layer of metal 12 having a relatively high coeicient of thermal expansion, a second layer of metal 14 having a relatively low coefficient of thermal expansion, and a third, intermediate layer of metal 16 preferably of high strength steel these layers of metal being metallurgically bonded together substantially throughout the interfaces 18 between the metal layers. As will be understood, the term metal as used herein is intended to include pure metal materials and metal alloys unless otherwise specified. 'As will also be understood, the metal layers of the thermostat metal 10 are metallurgically bonded together in any conventional way within the scope of this invention. For example, these metal layers are bonded together by rollbonding processes such as are described in U.S. Pats. No. 2,691,815, No. 2,753,623 and No. 3,646,591. Usually, the thermostat metal 10, is then further rolled as required to provide the thermostat metal, and each of the layers thereof, with the desired thickness and to place the materials of the metal layers in the customarily desired workhardened condition.

The metal layers 12 and 14 embodied in the thermostat metal 10 comprise various materials conventionally employed as high and low expansion materials in thermostat metals, the materials of the layers 12 and 14 4being selected with respect to their thermal expansion properties, moduli of elasticity and the like and being proportioned with respect to thickness relative to each other and to the layer 16 in the conventional way to provide the thermostat metal 10 with the flexivity desired. Preferably, for example, the materials and thicknesses of the metal layers 12 and 14 are selected with respect to the material and thickness of the metal layer 16 to provide the thermostat metal 10 with a high iexivity on the order of at least about 130 l0FI over a temperature range of 50 to 200 F. within the overall temperature range from about F. to about 1000F. In this regard, it will be understood that the term flexivity as used herein is defined in the well known manner established by the American Society for Testing Materials.

In accordance with this invention, the metal layer 16 is formed of a material, preferably high strength steel, which is characterized by a coeflicient of thermal expansion intermediate between the coeicients of thermal expansion of the materials embodied in the metal layers 12 and 14 and which is further characterized by strength properties substantially greater than the materials of layers 12 and 14. Preferably the material utilized in the metal layer 16 is characterized by a tensile strength of at least about 150,000 p.s.i. at room temperature and retains a substantial proportion of this tensile strength at temperatures well over l000 F. Preferably also the relative thickness of the layer 16 is selected such that the eiective tensile strength of the composite material 10 exceeds the unit tensile strength of either of the materials embodied in the metal layers 12 and 14. For example, the metal layer 16 preferably comprises at least about 20% of the total thickness of the composite material 10 for this purpose. In this regard, while it is not intended that the scope of this invention be bound to any specific theory, it is believed that, where the coefficient of thermal expansion of the metal layer 16 is intermediate the coeicients of thermal expansion of the metal layers 12 and 14, the thermal stresses to which the materials of layers 12 and 14 are subjected during heating tend to be signicantly decreased while the material of the metal layer 16 is being subjected to thermal stresses. Where the material of the metal layer 16 is then further characterized by substantially greater strength properties than the materials of metal layers 12 and 14, the resulting three-layer composite thermostat metal 10 displays signicantly greater resistance to permanent deformation when restrained while being heated to quite high temperatures. In this way, the metal layer 16 in the thermostat metal 10 appears to serve the dual function of reducing thermal stresses in the materials of metal layers 12 and 14 While increasing the effective strength of the composite thermostat metal, thereby making it possible to subject thermostat metals of this invention to restraint even While they are heated to quite high temperatures without risk of permanent deformation of the thermostat metals. .As a result, the thermostat metals of this invention are useful in many applications where conventional thermostat metals have tended to display variation in thermal response characteristics during use. Further, where the thermostat metals of this invention are adapted to utilize widely used thermostat materials in the metal layers 12 and 14 and widely used, readily available, high strength materials in the metal layer 16 as Will appear below, all of the materials are relatively inexpensive and the improved thermostat metals of this invention are readily made at very low cost.

In a preferred embodiment of this invention, for example, the layer 12 of the thermostat metal 10 is formed of a nickel-manganese-iron alloy having a nominal cornposition of 20% nickel, 6% manganese and the 'balance iron; layer 14 is formed of a nickel-iron alloy having a nominal composition of 36% nickel and the balance iron; and the layer 16 is formed of SAE 301 Stainless Steel having a nominal composition of 0.15 (max.) carbon, 2.00% (max.) manganese, 1.00% (max.) silicon, 16.00 to 18.00% chromium, 6.00 to 8.00% nickel and the balance iron. As will be understood, all material compositions are set forth herein by weight unless otherwise specified. These layer materials are metallurgically bonded together in any conventional way, are rolled to a total composite thickness of about 0.020 inches with the material layers 12, 14 and 16 comprising about 40%, 40% and 20% of the total composite thickness respectively, and, by means of the nal rolling of the composite material, the metals of each layer are placed in about 30% to 60% workhardened condition. Preferably, the thermostat metal is heated to a temperature in the range from about 200 F. to 1100 F. for about 1 to 5 hours for stress relieving at least the material of the metal layer 16. In this arrangement, the materials of layers 12, 14 and 16 display coelicients of thermal expansion of 11.1 6 in./in./ F., 0.7 10-6 in./in./ F. and 9.3 X10*6 in./in./ F. respectively in the temperature range from about 50 F. to 200 F.; the materials of the layers 12, 14 and 16 display moduli of elasticity (tension) of about 28,000,000 p.s.i., 21,400,000 p.s.i. and 28,000,000 p.s.i. respectively; the materials of the layers 12, 14 and 16 display respective tensile strengths in 30% to 60% Work-hardened condition in the temperature range from about 50 to 200 F. of about 124,000 to 145,000 p.s.i., 100,000 to 115,000 p.s.i. and 185,000 to 225,000 p.s.i.; the materials of the layers 12, 14 and 16 display respective yield strengths in 30% to 60% Work-hardened condition in the temperature range from about 50 to 200 F. of about 110,000 to 130,000 p.s.i., 95,000 to 112,000 p.s.i. and 150,000y to 205,000 p.s.i.; and the composite thermostat metal displays a flexivity of 138 10'7 in the temperature range from about 75 F. to 450 F. and a relatively lower exivity at temperatures above 450 F. It is found that, when this composite thermostat metal is formed into appropriate shape and is arranged to display substantial flexing movement during temperature variations in the range from 75 F. to 300 F. but is restrained against additional flexing movement when heated to higher temperatures, the thermostat metal is adapted to be heated to temperatures up to 700 F. in this restrained arrangement Without undergoing any permanent deformation and Without undergoing any change in thermal response characteristics. When these same materials are embodied in the metal layers 12, 14 and 16 in the same condition as above described, With the respective metal layer thicknesses comprising 37.5%, 37.5% and 25% of the total composite thickness, the resulting composite material displays a flexivity of 133 1()-'7 in comparable temperature ranges and displays even greater resistance to permanent deformation at elevated temperatures.

In other practical embodiments of the composite thermostat metal of this invention, other conventional high expansion materials are also utilized in the metal layer 12 of the thermostat metal. For example, the material of layer 12 alternately comprises an alloy having a nominal composition of 72% manganese, 18% copper and 10% nickel, an alloy having a nominal composition of 22% nickel, 3% chromium and the Ibalance iron, or an alloy having a nominal composition of 19.4% nickel, 2.25% chromium, 0.5% carbon, and the balance iron. These materials in the metal layer 12 display coeiiicients of thermal expansion in the temperature range from 50 to 200 F. of 14.8 l06 in./in./ F., 10.5 10 6 in./ in./ F., and 10.6 106 in./in./ F. respectively. Preferably Where these latter materials are used in the layer 12, the layer thickness comprises from about 20 to 30% of the total composite thickness. Similarly, the metal layer 14 alternately comprises any alloy of nickel and iron having a nickel content in the range from about 35.5 to 36.5

percent or other conventional alloys having coeflicients4 of thermal expansion of less than about 1.0 106 in./ in./ F. in the temperature range from about 50 F. to 200 F.

In accordance with this invention, the metal layer 16 alternately comprises any of the austenitic stainless steels commonly designated as the SAE 200 and 300 Series of Stainless Steels, these materials preferably being utilized in the metal layer 16 in at least partially work-hardened condition and preferably in Work-hardened, stress relieved condition. For example, useful materials for the metal layer 16 comprise the austenitic stainless steels designated SAE 201, 202, 302 or 304, these materials having a nominal composition of 0.15% (max.) carbon, 5.50 to 7.50% manganese, 1.00% (max.) silicon, 16.00 to 18.00% chromium, 3.50 to 5.50% nickel, 0.25% (max.) nitrogen, and the balance iron, a nominal composition of 0.15% (max.) carbon, 7.50 to 10.00% manganese, 1.00% (max.) silicon, 17.00 to 19.00% chromium, 4.00 to 6.00% nickel, 0.25% (max.) nitrogen, and the balance iron, a nominal composition of 0.15% (max.) carbon, 2.00% (max.) manganese, 1.00% (max.) silicon, 16.00 to 18.00% chromium, 6.00 to 8.00% nickel, and the balance iron, and a nominal composition of 0.08% (max.) carbon, 2.00% (max.) manganese, 1.00% (max.) silicon, 18.00 to 20.00% chromium, 8.00 to 12.00% nickel, and the balance iron respectively. Alternately, in other embodiments of this invention, the metal layer 16 comprises various age or precipitation hardenable stainless steel materials such as those commonly designated 17-7-PH Stainless Steel or PH-15-7 Mo Stainless Steel, these materials having a nominal composition of 0.07% carbon, 0.70% manganese, 0.40% silicon, 17.00% chromium, 7.00% nickel, 1.15% aluminum and the balance iron, and a nominal composition of 0.07% carbon, 0.70% manganese, 0.40% silicon, 15.00% chromium, 7.00% nickel, 2.25 molybdenum, 1.15% aluminum and the balance iron respectively. As will be understood, these latter materials are preferably utilized in the metal layer 16 with layer thicknesses comprising from about 20% to 30% of the total composite thickness and after heat treating in the range from albout 900 to 1150 F. for about l to 4 hours for hardening the materials. Other alternate materials for the metal layer 16 also include higher carbon steels such as those designated SAE 1050 to SAE 1095 which provide tensile strengths of 150,000 to 300,000 p.s.i. and moduli of elasticity of about 27,000,000 to 30,000,000 p.s.i. after appropriate heat treatments. These alternate materials for the metal layer 16 further include maraging steels such as those sold under the trademarks 5 Nimark I, Nimark 1I and Nimark 300, these materials having compositions (percentage by weight) as follows:

Nimark I N imark Il Ninark 300 Iron Bal. a a Carbon (max.)-.-.. 03 03 03 Manganese (max.) 10 10 10 Silicon (max.) 10 10 10 Phosphorus (max 01 01 01 Sulfur (max .01 .01 .01 Zirconium (m .03 .03 .03 Boron (max.). 003 003 003 Calcium (max.) 05 05 05 As will also be understood, these alternate materials for the metal layer 416 are adapted to display coefficients of thermal expansion in the range from about 5.0 6 in./in./ F. to about 9.0 10-6 in./in./ F. inthe 50 F. to 200 F. range and to display tensile strengths in the range from about 150,000 p.s.i. to about 300,000 p.s.i. or more, substantially greater than the tensile strengths displayed by the various materials suggested above for use in the metal layers 12 and 14. As will further be understood, these various proposed materials for the metal layers 12, 14 and 16 are preferably provided with appropriate layer thicknesses in the composite thermostat metals 10 in the conventional manner to provide the composite thermostat materials with ilexivities on the order of at least about 130x104 for at least a selected part of the range of temperatures from 100 F. to about 1000 F.

It should be understood that this invention includes all modifications and equivalents of the disclosed embodiments of this invention which fall within the scope of the appended claims.

We claim:

1. A composite thermostat metal having a flexivity of at least about 130 10'I over a temperature range of about 150 F. within the temperature range from about 100 F. to about 1000 F. for displaying substantial flexing movement during variation in the temperature of said composite material through said 150 F. temperature range, said composite material comprising a first layer of metal having a relatively high coeiiicient of thermal expansion and a selected tensile strength, a second layer of metal having a relatively low coefficient of thermal expansion and a selected tensile strength, and a third layer r0f metal sandwiched between and metallurgically bonded to said first and second layers of metal, said third layer of metal being selected from the group of steel alloys consisting of austenitic stainless steel alloys, precipitation hardenable stainless steel alloys, high carbon steel alloys, and maraging steel alloys having a tensile strength at room temperature of at least about 150,000 p.s.i., relatively greater than the tensile strengths of said materials of said first and second metal layers and having a coefficient of thermal expansion intermediate the coefficients of thermal expansion of said lirst and second layer materials, said third layer of metal having a thickness comprising at least about 20 percent of the total thickness of said composite material and said rst and second metal layers having selected thicknesses providing said composite material with said exivity, whereby said composite material is adapted to be restrained against iiexing movement while the temperature thereof is varied throughout the remainder of said temperature range from about 100 F. to 1000" F. without being subject to permanent deformation of said composite material, said first layer of metal being ganese, 18% copper and 10% nickel having a coeiiicient of thermal expansion of at least about 10.5 10-6 in./in./ F., said second layer of metal being formed'of an alloy selected from the group of alloys having nominal compositions, by weight, consisting of an alloy of between 35.5 and 36.5% nickel and the balance iron, and other metal alloys having coefficients of thermal expansion less than about 1.0 106 in./in./ F. in the temperature range from about 50 F. to about 200 F., and said third layer of metal having a coecient of thermal expansion in the range from about 5.0 l06 in./in./ F. to about 9.0 106 in./in./ F. in at least part of the temperature range from about F. to about 1000 F.

2. A composite thermostat metal as set forth in claim 6 wherein said iirst metal layer is formed of an alloy having a nominal composition, by weight, of 20% nickel, 6% manganese and the balance iron and comprising from 37.5 to 40% of the total thickness of said composite metal material, said second metal layer is formed of an alloy having a nominal composition, by weight, of 36% nickel and the balance iron and comprising from 37.5 to 40% of the total thickness of said composite metal material, and said third metal layer is formed of an austenitic stainless steel having a composition, by weight, of 0.15% (max.) carbon, 2.00% (max.) manganese, 1.00% (max.) silicon, 16.00 to 18.00% chromium, 6.00 to 8.00% nickel and the balance iron and comprising from 20 to 25% of the total thickness of said composite metal material, said metal layers being in from 30 to 60% work-hardened condition providing said composite thermostat metal with a exivity in the range from about 133 107 to about 138 107, said third layer material displaying a tensile strength in the range from about 185,000 to about 225,- 000 p.s.i.

3. A composite thermostat metal as set forth in claim 1 wherein said second layer of metal is formed of an alloy having a nominal composition, by weight, of between 35.5% and 36.5% nickel and the balance iron, and wherein said third metal layer is formed from a steel alloy selected from the group consisting of SAE 200 Series austenitic stainless steels having nominal compositions, by weight, of 0.15% (max.) carbon, 5.50 to 10.00% manganese, 1.00% (max.) silicon, 16.00 to 19.00% chromium, 3.50 to 6.00% nickel, 0.25% (max.) nitrogen, and the balance iron, SAE 300 Series austenitic stainless steels having nominal compositions, by weight, of 0.15% (max.) carbon, 2.00% (max.) manganese, 1.00% (max.) silicon, 16.00 to 20.00% chromium, 6.00 to 12.00% nickel, and the balance iron, SAE 1050 to 1095 high carbon steels, a precipitation hardenable stainless steel having nominal compositions, by weight, of 0.07% carbon, 0.70% manganese, 0.40% silicon, 15.00% chromium, 7.00% nickel, .2.25% molybdenum, 1.15% aluminum, and the balance iron, a precipitation hardenable stainless steel having a nominal composition, by weight, of 0.07% carbon, 0.70% manganese, 0.40% silicon, 17.00% chromium, 7.00% nickel, 1.15 aluminum, and the balance iron, a maraging steel having a nominal composition, by weight, of 19.50 to 20.50% nickel, 1.20 to 1.60% titanium, 0.15 to 0.35% aluminum, 0.40 to 0.60% columbium, 0.03% (max.) carbon, 0.10% (max.) manganese, 0.10% (max.) silicon, 0.01% (max.) phosphorous, 0.01% (max.) sulfur, 0.03% (max.) zirconium, 0.003% (max.) boron, 0.05% (max.) calcium and the balance iron, land maraging steels having a nominal composition, by weight, of 18.00 to 19.00% nickel, 7.00 to 9.50% cobalt, 4.70 to 5.10% molybdenum, 0.3 to 0.8% titanium, 0.05 to 0.15% aluminum, 0.03% (max.) carbon, 0.10% (max.) manganese, 0.10% (max.) silicon, 0.01% (max.) phosphor- 7 8 ous, 0.01% (max.) sulfur, 0.03% (max.) zirconium, References Cited 0.003% (max.) boron, 0.05% (max.) calcium and the UNITED STATES PATENTS balance iron, said third metal layers/having a thickness comprising from about 20 to 30% of the total thickness of said composite metal material and being in at least 5 3563712 2/1971 Zeigler 29 1955 partly hardened condition providing said third layer ma- 3219423 11/1965 Sears f -YT" 29; 19515 terial with a tensile strength in the range from about '150,- v 000 to 300,000 p.s.i. HYLAND BIZOT, Primary Examiner 

